Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to the detection of lesions within a body vessel. More specifically, the present invention is directed to the detection of vulnerable plaque legions by inserting a balloon into a body vessel, wherein the balloon is at least partially composed of material having temperature dependent properties which are optically detectable from within the balloon during use. The present invention utilizes a temperature responsive balloon material which exhibits a detectable change in at least one optical property such as color, reflectivity, optical density, polarization, etc. when in immediate proximity to the higher temperature of a vulnerable plaque lesion.
2. Description of the Related Art
It is widely recognized that plaques or lesions may be classified into three broad categories: calcified or hard plaque lesions, fibrous or soft lesions and inflamed soft lipid filled plaques or lesions. The diagnosis of the type of lesion drives the particular treatment of the lesion, whether it is removal of the lesion by rotablator, predilatation by balloon angioplasty, delivery of a stent, with or without predilatation, or the like.
In particular, the identification of inflamed plaques or lesions is important since these lesions are at greatest risk of rupture, which can lead to a large thrombus or blood clot, which can completely occlude the flow of blood through the artery, leading to injury of the heart or brain. An inflamed or vulnerable lesion is characterized by its cap thickness, lipid pool size and inflammation or temperature. This is discussed in great detail in U.S. Pat. No. 5,935,075, the entire contents of which are hereby incorporated by reference. As discussed in U.S. Pat. No. 5,935,075, considerable evidence indicates that plaque rupture triggers 60-70% of fatal myocardial infarctions. An inflamed plaque is hotter than the surrounding tissue. U.S. Pat. No. 5,935,075 relates to using an infrared fiber optic system to locate inflamed heat producing plaque by detecting the infra-red radiation absorbed by the balloon to a detector and signal fiber. However, the device described therein is very expensive, making it available in a limited number of procedures. What is needed is a more inexpensive method for classifying plaques or lesions, and in particular determining which plaques are hard, soft or inflamed, which drives the treatment after diagnosis.
In copending application Ser. No. 08/951,769, entitled Thermal and Stress Mapping of Body Lumens, commonly assigned and incorporated herein by reference in its entirety, there is described a technique for measuring lesion temperature by analyzing stress patterns in a lesion molding balloon which are revealed under a polariscope after the balloon has been molded to the lesion and then removed from the body for inspection. In this same application it has alternatively been suggested to use a balloon coating which changes color in accordance with a temperature experience.
Many materials are known which, within a defined temperature range change color in accordance with the then current temperature. Many such materials, however, are reversible, so that the observed color (within a material response time lag) is reflective of the real time temperature, not a past temperature history. Such materials would not be suitable to use in the system of application Ser. No. 08/951,769, since the lesion temperature is not read until the balloon has removed from the body.
As a result, it is clear that there is a continued need for a relatively inexpensive means of detecting vulnerable plaque within the body using a balloon having a temperature responsive material which produces a detectable change which may be detected and/or observed while the balloon remains in the body.
This invention provides for a balloon catheter which may be inserted into a body lumen and advanced to the suspected location of a vulnerable plaque lesion. At least a portion of the balloon material is comprised of a temperature responsive material such as a thermochromic cholesteric liquid crystal material or materials which produces an optically detectable property change when the material is exposed to increases in temperature. For instance thermometers using cholesteric liquid crystal such as those available from Hallcrest, Inc. are known to display a specific color when a given temperature is reached or exceeded. Materials exhibiting a color change or other type of detectable change in an optical property, such as: a change in polarization, optical density, reflectivity, etc.; when the material is subjected to a predetermined temperature may be suitable for use in the present invention.
Because the balloon includes material having such temperature indicating property, or properties, when the balloon is inflated to be in contact with a vulnerable plaque lesion, the higher temperature of the lesion will be detected by analyzing a beam of light which is directed on to the suspected lesion site and the balloon material in contact therewith. In at least one embodiment of the invention the light may allow a user to directly observe a change in the balloon material such as a color change, alternatively a detector may be used to detect changes such as a change in the materials reflectivity as a result of the increase in temperature.
Because many thermochromic cholesteric liquid crystal materials provide a real-time indication of temperature, it is desirable to observe the property change(s) of the balloon material while it is in contact with the lesion site. In at least one embodiment of the present invention, the balloon material may be directly observed in situ, from within the expanded balloon, by providing the catheter with at least one light source which may be used to transmit light into the balloon to illuminate the balloon interior so that any potential coloring, or other physical change, of the material may be detected by a light detecting device or a viewing device to provide for direct observation by a practitioner. By detecting and/or viewing the color, or other property change in the material or light reflected therefrom, the practitioner is able to confirm the location of a lesion in real time. If no color change or other property change is detected, the balloon may be deflated and advanced to another site, where the balloon may once again be inflated and potential changes observed.
In light of the above, the present invention provides for a catheter that may provide real time location and imaging of vulnerable plaque lesions.
In at least one embodiment of the invention a catheter is provided which has a balloon, the balloon being capable of repeated inflation and deflation so that with a single use the catheter may be used to locate one or more lesions which may be located along the length of a body vessel or lumen.
In at least one embodiment, the balloon catheter of the present invention may be incorporated into other devices and/or incorporate other devices. For example the present invention may be equipped with a second balloon which may be employed to deliver a stent to a lesion site detected by the thermochromatic balloon of the present invention. Such hybrid devices could allow a single catheter to be used for detection and treatment of a lesion, thereby avoiding the need to employ multiple catheters and thus multiple medical procedures.
In addition to the apparatus described above, the present invention as described above is directed also to the inventive method described which requires advancing the balloon catheter to the suspected site of a lesion, inflating the balloon to contact the lesion, after an equilibration time illuminating the balloon surface from within the balloon by transmission of light from a light source positioned alternatively within the balloon or outside of the balloon, directing the light onto the portion of the balloon in contact with the lesion, and then detecting the light reflected from the balloon material with a detector or through direct visual inspection.
Direct detection and/or observation of changes in the balloon material via reflected light may allow a user to produce a temperature map of the lesion. By referencing the shape of the lesion as indicated by the observed deformation of the inflated balloon and the optical properties of the balloon material, a temperature map may be generated which can be used to determine whether a lesion is an inflamed vulnerable lesion which is at greatest risk of rupture. The observed properties of the material at a lesion site may also be used to determine whether the lesion is a hard calcified lesion or other type of lesion.